Added the env and evaluation for addition and subtraction functions

src/macros.rs

@@ -0,0 +1,8 @@
+macro_rules! insert_symbol {
+    // Takes the env and a symbol in &str form, then it takes a variable list,
+    // of arg types and then a fn to run over them.
+    (&env:expr, &symbol:expr) => {
+        // The macro will expand into the contents of this block.
+        println!("Hello!")
+    };
+}